Heart monitoring apparatus for a motor vehicle

ABSTRACT

The EKG signal of the vehicle operator is sensed through electrodes mounted in the steering wheel and conditioned by amplifying and band pass filtering means to produce a signal which is substantially the QRS complex of the EKG signal. The width of the QRS complex is continually compared with the nominal width for the vehicle operator and an indication of whether the width is narrower or wider is provided to the operator.

United States Patent [191 McIntosh 1 May 8, 1973 s41 HEART MONITORINGAPPARATUS 3,144,019 8/1964 Haber ..128/2.06 A FOR A MOTOR VEHICLE3,267,934 8/1966 Thornton.... ...128/2.06 A 3,460,527 8/1969 Karsh128/206 A [75] Inventor: Duane E. McIntosh, Palmyra, WIS. 3 524 442 1970Honh 12 20 A 73 Assignee: General Motors .c p 3,612,041 10/1971 Ragsdale..128/2.06A

D t 't,M' h. 6 ml 10 Primary Examiner-William E. Kamm [22] Filed: Oct.4, 1971 Attorney-Eugene W. Christen et a1.

21 A l. N 4 I 1 PP 0 185,9 2 [57] ABSTRACT The EKG signal of the vehicleoperator is sensed fi 'g "128/106 128/206 through electrodes mounted inthe steering wheel and [58] Fieid A 2 06 E conditioned by amplifying andband pass filtering means to produce a signal which is substantially the128/206 340/279 QRS complex of the EKG signal. The width of the QRScomplex is continually compared with the [56] References Cited nominalwidth for the vehicle operator and an indica UNITED STATES PATENTS tionof whether the width is narrower or wider is provided to the operator.2,816,282 12/1957 Sewell ..340/279 3,049,090 8/1962 Bergen ..340/279 3Claims, 5 Drawing Figures SATURATION c z l nouea DRIVEN EDGE PULSE FULLWAVE GENERATOR RECTIFIER 3'8 0 OUNTER AND LOGIC FIXED PULSE STRETCHERADJUSTABLE PULSE STRETCHER DIFFERENTI POWER RATIOMETER PATENTED AY 81msum 1 0r 3 l6 1 l6 SATURATION SIGNAL EDGE PULSE DRIVEN CONDlTIONE FULLWAVE GENERATOR RECTIFIER 3'8 COUNTER AND LOGlC i2 FlXED PULSE Z5STRETCHER .J ERROR Z4! 6 MULTIPLIER \ADJUSTABLE 2 PULSE 3 STRETCHERDIFFERENTIAL.

POWER f RATIOMETER INVENTOR' f flzmne 5 fifclvz'asri ATTORNEY PATENTHAY' 81973 SHEET 2 BF 3 ie i272 1N VENTOR. flaazze d/Wefzziogk wdflfmATTORNEY PATENTEDHAY 81973 sum 3 {1F 3 j l l l TRUTH TABLE ATTORNEYHEART MONITORING APPARATUS FOR A MOTOR VEHICLE This invention relates toa cardiac monitor and more particularly to apparatus for continuouslymonitoring the electrocardiac signal of the operator of a motor vehicle.

Coronary artery disease is a leading cause of death in the adultpopulation. This disease starts early in childhood and is found in asignificant percentage of American males between ages 18 and 21. Thedisease progresses in asymptomatic form and may culminate in anginapectoris, Le. a heart attach, or sudden death from a cardiac arrythmia.The latter is believed responsible for a significant numberof'automobile accidents. Early detection of the disease could result inmore successful treatment, however, this is seldom accomplished becauseearly electrocardiae abnormalities may occur only during periods ofstress and then only transiently. Most often the abnormality is onlydiscovered after damage has already occurred.

Driving an automobile is a daily occurrence with a significantpercentage of the population. For many American working males morningand evening motoring to and from work has become a daily occurrence.Accordingly, the automobile provides a readily available environment fordynamic testing of the physiological well being of many individuals.

With the foregoing in mind, it is an object of the present invention toprovide apparatus particularly suitable for continuously monitoring theelectrocardiac signal of a motor vehicle operator during vehicleoperation.

It is another object of the present invention to provide apparatus fordetecting and indicating any significant change in the electrocardiacsignal of an individual.

It is another object of the present invention to provide a cardiacmonitor for a motor vehicle which includes display circuitry which isbiased in favor of indicating normal electrocardiac activity of thevehicle operator to prevent erroneous abnormal indications which mightresult from the dynamic conditions under which the monitoring isperformed.

It is another object of the present invention to provide a cardiacmonitor for a motor vehicle operator which is highly insusceptible toextraneous electrical signals encountered during normal vehicleoperation.

In accordance with the present invention the electrical activity of theheart present at the hands of the vehicle operator is picked up byelectrodes located in the steering wheel of the vehicle. Signalconditioning means amplify, filter and differentiate the EKG signal.This conditioned signal is rectified by a saturation driven full waverectifier and fed to pulse generating means which produces a pulse trainhaving a pulse corresponding to each edge of the rectified signal.Circuitry responsive to the generated pulses performs a reasonablenesstest based on the number of pulses generated, to further limit thepossibility of processing and indicating spurious data. Each of thepulses generated are applied to the input of a fixed pulse stretcherwhich provides an output pulse of time duration proportional to timeduration between the rising edge of the first generated pulse and thefalling edge of the last generated pulse which in turn is related to thewidth of a scaled version of the QRS complex of the EKG signal. Theoutput of the pulse stretcher is compared with a pulse output which isproportional to the nominal width of the QRS complex for the vehicleoperator and an error signal is generated. A proportional pulsestretcher is provided to multiply the error signal which is used todrive one of two thermal integrators, depending upon whether the errorsignal represents a wider or narrower than nominal QRS width for theoperator. The thermal integrators provide long term integration of theerror signal generated. The difference in output of the thermalintegrators is used to drive a differential power ratiometer to providean indication of the amount and direction of the deviation in QRScomplex width.

A more complex understanding of the present invention may be had fromthe following detailed description which should be read in conjunctionwith the drawings in which:

FIG. 1 is a functional block diagram of the apparatus of the presentinvention;

FIGS. 2a and 2b are a schematic diagram of the apparatus of the presentinvention;

FIG. 3 shows a truth table for the logic employed in the apparatus ofthe present invention;

FIG. 4 shows waveforms at various junctions in the apparatus andprovides an aid in understanding the invention.

Referring now to the drawings and initially to FIG. 1, the cardiacmonitor of the present invention comprises electrodes 10 and 12 ofgenerally semicircular shape which are imbedded in the motor vehiclesteering wheel and pick up the electrocardiac signal present between thehands of the vehicle operator during operation of the vehicle. Thesteering wheel is preferably made of a relatively good conductor such asfor example, a silver-silver chloride material. While each electrode 10and 12 is shown as covering substantially one-half the steering wheelcircumference, other arrangements are permissible. For example, theelectrodes may cover only a small area in locations most often grippedby the operator during operation of the vehicle.

The electrodes 10 and 12 are connected to signal conditioning means 14which amplify the difference in potential existing between the hands ofthe operator; provide a substantial attenuation of signals of afrequency on either side of a 30 Hz. to 100 Hz. band. The resultingsignal consists primarily of the ventricular depolarization waveforms(QRS complex) the character of which is somewhat altered by the signalconditioner 14 but which is of a width proportional to the actual QRScomplex. The signal is further processed by saturation driven full waverectifier means generally designated 16 which includes upper and lowerlevel detectors and gating means for produc- 3 ing a pulsating output.The pulsating output passes through a gate NAND I8 to an edge pulsegenerator 20 which generates pulses on the rising and falling edges ofthe rectified signal.

Each pulse from 4 the generator 20 triggers a fixed pulse stretcher 22which is used to represent the width of the QRS complex. While the widthof this pulse is not a clinical representation of the true width of theQRS complex, it is as previously mentioned, proportional to the truewidth of the QRS complex. The first pulse from the generator 20 alsotriggers an adjustable pulse stretcher 24 which produces an output pulseof adjustable duration proportional to the nominal width of the QRScomplex for the particular operator of the vehicle.

The outputs of the pulse stretchers 22 and 24 are fed to a comparator 26which provides an output equal to the difference between the input pulsewidths. The output of the comparator 26 is applied to a proportionalpulse stretcher or error multiplier 28 which multiplies the error signaland also disables gate 18 to prevent any extraneous signals fromtriggering the generator 20. Depending on whether the QRS intervalmeasured is greater than or less than the nominal period established bythe stretcher 24, one of a pair of NAND gates 32 or 34 will be enabledto pass the multiplied error signal to a differential power ratiometer36 which integrates the error signal to a differential power ratiometer36 which integrates the error signal over a large time interval andprovides an indication of any long term variation of the detected EKGsignal from the nominal EKG signal of the vehicle operator.

The output of the generator 20 is also fed through counter and logiccircuitry 38 which determines, based on the number of pulses counted,whether the pulses being generated are a result of the EKG signal orfrom some extraneous source. The counter and logic 38 provide anenable/disable signal to the pulse stretchers 22 and 24 so that acomparison is made only when the data is reasonably related to the QRScomplex.

Referring now to FIG. 2a, input leads 40 and 42 connect the signalconditioning means 14 to the electrodes and 12. The signal conditioningmeans 14 include a high input impedance AC coupled differentialamplifier comprising a pair of operational amplifiers 44 and 46 havingnon-inverting and inverting inputs designated and respectively. Theelectrodes 10 and 12 are connected respectively to the non-invertinginputs of the amplifiers 44 and 46. The amplifiers 44 and 46 have theirnon-inverting inputs grounded through resistors 48 and 50 respectivelyand have their output terminals connected with the inverting inputterminals through resistors 52 and 54 respectively. Capacitors 56 and 58are connected from the output to the inverting input of the amplifiers44 and 46 respectively to heavily attentuate extraneous data of afrequency over 100 cycles. The rest of the data appears at the invertinginputs of the amplifiers 44 and 46 and at approximately a gain of l. Acapacitor 60 connects the inverting inputs of the amplifiers 44 and 46together and heavily attenuates the very low frequency inputs receivedat the non-inverting inputs of the amplifiers 44 and 46. Thenon-inverted data appearing at the output of the amplifiers 44 and 46 isfed back to the inverting input of the other amplifier through thecapacitor 60 so that in effect, the difference in potential appearingbetween the hands of the operator is applied as the two inputs to botham plifiers 44 and 46 with this difference being amplified at the outputof each amplifier 44 and 46 which is then fed back to the otheramplifier permitting a gain of higher than 1 to be achieved on the highfrequency data from the heart pulse while still maintaining a high inputimpedance. The outputs of the amplifiers 44 and 46 are AC coupledthrough capacitors 62 and 64 which removes minor DC offsets in theamplifiers 44 and 46 and are applied to a summing amplifier 66 havingits non-inverting input grounded through a resistor 68 and its outputconnected to its inverting input through a resistor 70. The output ofamplifier 66 is connected to the non-inverting input by a capacitor 72and is connected to ground through a resistor 74 and a capacitor 76 tofurther attenuate frequencies below 30 Hz. and above 100 Hz. The EKGwaveform A shown in FIG. 4 appears at the output of the signalconditioner 14 as shown in waveform B in FIG. 4 and is applied to thefull wave rectifier 16.

The full wave rectifier 16 comprises a pair of operational amplifiers 78and 80 which serve as level detectors. The output of amplifier 66 isapplied to the noninverting input of the amplifier 78 and the invertinginput of the amplifier 80 through resistors 82 and 84 respectively. Thelevel at which the amplifiers 78 and 80 switch states is determined bythe voltage appearing at the inverting input of the amplifier 78 and atthe noninverting input of the amplifier 80. The voltage at the invertinginput of the amplifier 78 is established by a voltage divider networkgenerally designated 86 comprising resistors 88, 90 and 91. The voltageestablished at the non-inverting input of the amplifier 80 is determinedby a voltage divider network 92 comprising resistors 94, 96 and 98.Zener diodes 100 and 102 regulate the voltage at the output of theamplifier 78 and 80 respectively to a magnitude consistent with thelogic circuitry employed. The output of amplifiers 78 and 80 isconnected with a NAND gate 104. As shown in the truth table in FIG. 3,the output of the NAND gate 104 is a logic l whenever either of theinputs to the gate 104 are a logic 0" and is a logic 0 only when bothinputs to the gate 104 are a logic l The positive voltage levelestablished at the non-inverting input of the amplifier 80 maintains theoutput of the amplifier 80 at a logic l except for that interval of timewhen the input signal applied to the inverting input is above the levelestablished at the non-in verting input at which time the output of theamplifier 80 switches to a logic 0. Similarly, the output of theamplifier 78 is a logic l due to the inversion of the negative voltageapplied at the inverting input and remains a logic l except for theinterval of time that the input signal is below the negative voltageestablished at the inverting input. Thus the inputs to gate 104 arenormally logic l s providing a logic 0" output. Whenever either of theoutputs of the amplifier 78 or 80 drop to a logic 0 the output of thegate 104 switches to a logic 1. Consequently, the signal applied to theinput of the amplifiers 78 and 80 appears at the output of the gate 104as the pulsating waveform C shown in FIG. 4 containing a pulse for eachexcursion of the input signal above and below each of the voltage levelsestablished by the network 86 and 92. The output of the gate 104 isapplied as one input to the NAND gate 18, the other input of which is alogic 1 for reasons which will be explained hereinafter. Accordingly,the output of the gate 18 is a logic 0, whenever the output of the gate104 is a logic I; and switches to a logic l whenever the output of thegate 104 switches to a logic O." /z

The output of the gate 18 is applied to the input of a single shot ormonostable multivibrator 108 of pulse generator 20 (FIG. 2b)and isinverted by a NAND gate 110 and applied to the input of a second singleshot or monostable multivibrator 112. The 6 terminal of themultivibrator 108 switches from a logic l to a logic 0 on the risingedge of the output of the gate 18. The 6 terminal of the multivibrator112 switches from a logic l to a logic 0" on the rising edge of theoutput of the gate 1 which corresponds to the falling edge of the outputof the gate 18. The Q terminals of the multivibrators 108, 112 areconnected as inputs to a NAND gate 114 which provides at its output thetrigger pulse train shown in FIG. 4 (waveform D) corresponding to therising and falling edges of each pulse in the pulse train output of thegate 18.

The gate 114 is connected to the input of a single shot or monostablemultivibrator 116 of pulse stretcher 22 which has its Q output terminalconnected to the input of a single shot or monostable multivibrator 118of adjustable pulse stretcher 24. During their stable state, therespective Q and Q outputs of the multivibrator 116 and 118 are logic 0and logic l The first pulse from the pulse generator switches the Qoutput of multivibrator 116 to a logic l which switches the Q output ofthe multivibrator 118 to a logic 1. The unstable state of themultivibrator 116 is of sufficient duration so that the multivibrator116 will not return to its stable state during the time interval betweenpulses from the pulse generator 20. Thus, a fixed time interval afterthe final pulse from the pulse generator 20 the multivibrator 116returns to its stable state as shown in the waveform E of FIG. 4. Themultivibrator 118 has an unstable state which is adjustable by varyingthe resistance of a series RC network comprising the resistor 120 andthe capacitor 122 to produce the waveform F of FIG. 4. By varying theresistor 120 the cardiac monitor may be programmed for the particularvehicle driver as will be explained more fully hereinafter.

The 6 output terminal of the multivibrator 116 is applied to the clockinput of a delay or D type flip-flop 124 which transfers the dataappearing at its D terminal to its Q output terminal on the rising edgeof a clock pulse. The 6 terminal of the multivibrator 118 is connectedwith the clock terminal ofa D type flip-flop 126. The Q terminal of themultivibrator 116 is applied to the D terminal of the flip-flop 126through a NAND gate 128 while the Q terminal of the multivibrator 118 isapplied to the D terminal of the flip-flop 124 through a NAND gate 130.The other inputs to the gates 128 and 130 are received from the counterand logic circuitry 30 and are assumed to be a logic l at this point inthe discussion. The set terminals S of the flip-flops 124 and 126 areconnected with the outtyt of the pulse generator 20 so that the outputat the 0 terminals of the flip-flops 124 and 126 are set to a logic 0 bythe pulses from the pulse generator 20. If the Q output terminal of themultivibrator 116 is a logic l, i.e. the multivibrator 116 is in itsunstable state, logic l 's are applied to both inputs of the gate 128and a logic 0" appears at the D terminal of the flip-flop 126. When themultivibrator 116 reverts to its stable state, a logic "0" appears atone input of the gate 128 producing a logic l on the D terminal offlip-flop 126. Similarly, while the multivibrator 118 is in its unstablestate, logic l s appear at the inputs to gate 130 producing a logic 0 atthe D terminal of the flip-flop 124. When the multivibrator 118 revertsto its stable state a logic 0 appears at one input of the gate producinga logic l at the D terminal of flip-flop 124.

If the multivibrator l 16 reverts to its stable state while themultivibrator 1 18 is still running, indicative of the fact that thedata detected was of shorter duration than nominal, a logic 0 is clockedinto the Q terminal of flip-flop 124 and consequently a logic l isproduced at the 6 terminal of the flip-flop 124. Then when themultivibrator 1 18 does revert to its stable state, a logic l is clockedinto the Q terminal of flipflop 126 maintaining a logic 0" on the 6terminal of the flip-flop 126. On the other hand, if the multivibrator118 reverts to its stable state, while the multivibrator 116 is stillrunning, indicative of the fact that the data detected was of longerduration than'nominal, a logic l is clocked into the 6 terminal of theflip-flop 126. Then when the multivibrator 1 16 does revert to itsstable state a l is clocked into the Q terminal of the flip-flop 124maintaining a logic 0 at the 6 terminal of the flip-flop 124. Thus theoutputs at the 6 terminals of the flip-flops 124 and 126 provide anindication of whether the data detected was of shorter or longer thannominal duration.

The comparator 26 comprises NAND gates 132, 134 and 136. The NAND gate132 has inputs connected to the 6 terminal of the flip-flop 126 and theQ terminal of the multivibrator 116. The gate 134 has its inputsconnected to the 6 terminal of the flip-flop 124 and the Q terminal ofthe multivibrator 118. The gate 136 has its inputs connected to theoutputs of the gates 132 and 134. The first pulse from the pulsegenerator 20 sets the flip-flops 126 and 128 placing a logic 0 at the Qterminals thereof and switches the Q terminals of the multivibrators 116and 118 to a logic l Thus the outputs of the gates 132 and 134 areinitially a logic l and the output of the gate 136 is a logic 0. Tloutput of the gate 136 switches to a logic 1" if the Q terminals ofeither of the flip-flops 124 or 126 switches to a logic l which occurswhen one of the multivibrators 116 and 118 reverts to its stable state.The output of the gate 136 will revert to a logic 0 when the other ofthe multivibrators 116 and 118 subsequently reverts to its stable state.For example, if the width of the data detected is less than nominal themultivibrator 116 reverts to its stable state while the multivibrator118 is still running placing a logic l at the Q terminal of flip-flop124 which switches the gate 134 to a logic 0 causing the gate 136 toproduce a logic the 1. When the multivibrator l 18 reverts to its stablestate the logic 0" input to the gate 134 switches its output to a logicl causing the output of the gate 136 to switch to a logic O." Similarly,if the width of the data detected is longer than nominal, the Q terminalof the flip-flop 126 switches to a logic l when the multivibrator 118reverts to its stable state providing a logic 0" input to the gate 136from the gate 132. This produces a logic l at the output of the gate136. When the multivibrator 116 reverts to its stable state the logic 0"input to the gate 132 switches its output to a logic l causing theoutput of the gate 136 to switch to a logic 0. Accordingly, the timeduration of the logic l output of the gate 136 is proportional to thedifference in expiration time of the multivibrators 116 and 118 andtherefore proportional to the difference between the nominal and thedetected data interval.

The error multiplier 28 is a pulse stretcher which includes a capacitor156 which is connected to the output of the gate 136 through a diode 158and a resistor 160. The capacitor 156 is connected to the non-invertinginput of a differential amplifier 162 which has its inverting inputconnected to a voltage divider 164 which establishes the threshold levelof the amplifier 162. As the capacitor 156 charges above the thresholdlevel of the amplifier 162, the output of the amplifier 162 switchesfrom a logic to a logic 1. When the output of the gate 136 switches to alogic 0 the capacitor 156 discharges through a resistor 166. Thedischarge time for the capacitor 156 is substantially greater than thecharge time so that the output of the amplifier 162 remains at a logiclevel l for a much longer period of time than does the output of thegate 136. Resistors 168 and 170 and zener diode 172 clamp the outputvoltage of amplifier 162 to a value compatible with the logic employed.

The output of the amplifier 162 is one input to NAND gate 32 and 34. Theother input to the gate 32 is from the Q terminal of flip-flop 124,while the other input to the gate 34 is from the 6 terminal of flip-flop126. Therefore, when the flip-flop 124 and 126 are set by the pulsegenerator both inputs to the gates 32 and 34 are logic Os producinglogic l outputs. If the width of the data detected is greater than noiinal the gate 34 receives a logic 1 input from the Q terminal of theflip-flop 126 and a logic l input from the amplifier 162 while if thewidth of the data detected is less than nominal, the gate 32 receives alogic 1 "input from the Q terminal of the flip-flop 124 and a logic linput from the amplifier 162. Thus, the width of the error pulse outputof the comparator 26, after stretching by the error multiplier 28 ifapplied to one of two channels depending upon whether the error resultsfrom a wider or narrower than nominal QRS complex.

The differential power ratiometer 36 comprises a switching amplifier 178which energizes a heater 180 whenever the output of the gate 32 switchesfrom a logic 1 to a logic 0. A switching amplifier 182 energizes aheater 184 whenever the output of the gate 34 switches from a logic l toa logic 0. The heaters 180 and 184 drive thermocouples 186 and 188respectively, which are connected with the inverting and noninvertinginputs of a differential amplifier 190 through resistors 192 and 194respectively. The inverting and non-inverting inputs of the amplifier190 are connected to ground through resistors 196 and 198 respectivelyand a resistor 200 connects the output of the amplifier 190 to theinverting input. The output of the amplifier 190 drives a meter 202which is grounded through a resistor 204. The meter 202 provides amid-range reading when the inputs to the differential amplifier are thesame and provides a reading on either side of midrange indicative of aQRS complex of width greater than or less than the nominal widthestablished by the multivibrator 118. The output of the amplifier 162 isalso fed through an inverter comprising NAND gate 205 to inhibit thegate 18 while the data detected is being processed in the ratiometer 36.

The nominal time interval established by the multivibrator 118 isadjustable by varying the resistor 120. Accordingly, by adjusting theresistor 120 until a midrange indication is obtained on the meter 202,the apparatus of the present invention may be set for the par ticularindividual operating the vehicle and will thereafter provide anindication of any significant deviation in the QRS complex of the EKGsignal of the individual.

The counter and logic circuitry 38 provides a means for determiningwhether the output of the pulse generator 20 is reasonably related tothe EKG signal rather than some extraneous input and includes a countercomprising a plurality of D type flip-flops 206, 208, 210 and 212. The Qterminal of each flip-flop is connected with the clock terminal of thefollowing flip-flop while the 6 and D terminals of each flip-flop areconnected together. The clock terminal of the flip-flop 206 is connectedwith the pulse generator 20 at the output of the gate 114. The output ofthe gate 114 is inverted by a NAND gate 214 and applied as one input toa NAND gate 216. The other input of the gate 216 is connected with the 6terminal ofthe multivibrator 1 16. The 0 terminals of flip-flops 208 and210 provide inputs to a NAND gate 218. The Q terminal of flip-flop 212and the output of the gate 218 provide inputs to a NAND gate 220 theoutput of which is inverted by NAND gate 222 and applied as one input tothe gates 128 and 130.

Prior to generation of a pulse from the generator 20 the 6 terminal ofthe multivibrator 116 is at a logic 1 and the output of the gate 214 isa logic l providing a logic 0 at the output of gate 216. The logic 0output of the gate 216 sets the flip-flops 206, 208, 210 and 212 placinga logic l at their respective Q terminals and a logic 0 at theirrespective Q and D terminals. This places logic l at the input to thegate 218 providing a logic 0 at its output. Thus a logic 0 and a logic lare applied to the inputs of gate 220 providing a logic 1 which isinverted by gates 222 to provide a logic 0 input to gates 128 and 130.The first output pulse from the generator 20 is applied to the clockinput of the flip-flop 206 but has no effect since the flip-flop 206 isheld in a set condition at the time of arrival of the pulse. The firstoutput pulse also triggers the multivibrator 116 and in turn themultivibrator 118 providing a logic 0 at the 6 terminal of multivibrator116 which raises the output of the gate 216 to a logic l releasing thecounter whichis now free to count the succeeding pulses from thegenerator 20. On the third pulse from the generator 20 the Q terminal ofthe flipflop 208 switches from a logic 1 to a logic 0 which places alogic 1 at the output of the gate 222 thus enabling the gates 128 and130. The gates 128 and will remain enabled until a logic 0 appears atthe Q terminal of the flip-flop 212, which occurs on the 17th pulse fromthe generator 20.

It will be appreciated that the counter establishes a window which inthe example given, wherein the counter comprises four flipilops, permitsthe evaluation of only those electrical input signals which result inmore than two and less than seventeen output pulses from the generator20. A noise spike producing two pulses from the generator 20 wouldtrigger the multivibrators 116 and 118 but would not affect the outputat the gate 222 which would remain at a logic 0" maintaining a logic lat the output of gates 128 and 130. When the multivibrators 116 and 118expire a logic 0" is maintained at the 6 terminals of the flipflops 124and 126 which disables the gates 174 and 176 preventing energization ofthe heaters and 184.

Similarly, if the vehicle is located in an area near a 60- cycletransformer for example, or if the operator taps his fingers on thesteering wheel in a fashion that causes the generator to produce 17 ormore output pulses than the Q terminal of the flip-flop, 212 will switchto a logic 0 placing a logic 0 at the output of the gate 222 therebypreventing energization of the heaters 180 and 184 in the same manner asdescribed above. It will be understood that the width of the windowestablished by the counter may be varied by changing the number offlip-flops.

While the invention has been described in connection with apparatusfor,monitoring the EKG signal it will be apparent to those skilled inthe art that the technique employed of monitoring for change in the EKGsignal is applicable to other complex waveforms related to thephysiological condition of the individual.

I claim:

1. Apparatus for monitoring the physiological condition of an occupantof a motor vehicle during vehicle operation comprising;

pickup means for sensing an electrical signal related to thephysiological condition of the vehicle occu pant,

signal conditioning means connected with said pickup means,

rectifier means connected with said signal conditioning means fordeveloping an output pulse corresponding to each excursion of theconditioned signal above and below respective upper and lower-voltagelevels,

pulse generating means for generating a trigger pulse traincorresponding to the leading and trailing edge of each output pulse,

pulse stretcher means responsive to said trigger pulse train fordeveloping a pulse of duration greater by a fixed time interval than theduration of said trigger pulse train, adjustable pulse stretcher meansresponsive to the first pulse in said trigger pulse train for developinga pulse of adjustable duration,

comparator means responsive to the output of said fixed and adjustablepulse stretchers for developing an error pulse output of durationproportional to the difference in the duration of the output of saidfixed and adjustable pulse stretcher means,

means including ratiometer means responsive to said error signal forindicating the magnitude and polarity of said error signal,

means for manually adjusting the output of said adjustable pulsestretcher to produce a null output from said ratiometer means wherebysaid ratiometer indicates any significant change in the width of theoutput signal of said signal conditioning means subsequent to adjustmentof said adjustable pulse stretcher,

means for counting the number of pulses in said trigger pulse train andfor inhibiting the output of said fixed and adjustable pulse stretcherswhen the number of pulses in said pulse train are less than or greaterthan a predetermined number.

2. In a motor vehicle provided with a steering wheel, apparatus formonitoring the electrocardiac signal of the operator of the vehicle andfor indicating to said operator a change in said signal from the nominalsignal of the operator, said apparatus comprising;

a pair of electrodes mounted in said steering wheel for sensing theelectrocardiac signal present between the hands of the operator,

signal conditioning means comprising first and second amplifiers havingtheir non-inverting inputs connected with respective ones of saidelectrodes, a capacitor interconnecting the inverting inputs of saidfirst and second amplifiers, a resistancecapacitance networkinterconnecting the output of each of said first and second amplifiersto their respective inverting inputs, a third amplifier having itsrespective non-inverting and inverting inputs capacitively coupled tosaid first and second amplifiers, a third resistance capacitance networkinterconnecting the output and inverting input of said third amplifier,

full-wave rectifier means comprising first and second level detectingmeans responsive to the output of said signal conditioning means fordeveloping a pulse train containing a pulse for each excursion of theinput signal above and below a positive and a negative voltage level,

pulse generating means for developing a trigger pulse corresponding toeach of the leading and trailing edges of said pulse train,

pulse stretcher means comprising a single shot multivibrator triggerableto a semi-stable state in response to a trigger pulse from said pulsegenerator means and returning to its stable state a fixed interval oftime thereafter, a second single shot multivibrator triggerable to itssemi-stable state in response to the triggering of said first singleshot multivibrator and returning to its stable state after an adjustabletime interval,

differential power ratiometer means comprising first and secondchannels,

gating and storage means responsive to the state conditions of saidfirst and second monostable multivibrators for developing an errorsignal for application to one or the other of said first and secondchannels depending upon which of said monostable multivibrators firstreturns to its stable state and proportional to the difference in theduration of the unstable state of said first and second monostablemultivibrators,

means for counting the number of trigger pulses from said pulsegenerator and for inhibiting said gating means when the number oftrigger pulses are less than or greater than a predetermined number. 3.ha motor vehicle provided with a steering wheel,

apparatus for monitoring for any change in the electrocardiac signal ofthe operator of the motor vehicle during vehicle operation comprisingfirst and second electrodes mounted in said steering wheel 'for sensingthe electrocardiac signal existing between the hands of the vehicleoperator,

signal conditioning means comprising amplifying and filtering meansconnected across said electrodes for developing a scaled version of theQRS complex of said electrocardiac signal, means including full waverectifying means and pulse generating means for developing a group oftrigger pulses over an interval of time related to the width of the QRScomplex of said electrocardiac signal, pulse stretcher means responsiveto said trigger pulses for developing a pulse of duration greater by afixed time interval than the duration of said group of trigger pulses,

adjustable pulse stretcher means responsive to the first pulse in saidgroup of trigger pulses for developing a pulse of duration correspondingto the nominal width of the QRS complex of the electrocardiac signal ofthe vehicle operator,

comparator means responsive to the output of said fixed and adjustablepulse stretchers for developing a pulse output of duration proportionalto the difference in the duration of the QRS complex being monitored andthe nominal QRS complex of the vehicle operator,

error amplifying means connected with said comparator means,

indicator means having first and second input channels and providing anindication of the average magnitude and direction of any deviation ofthe sensed QRS complex from the nominal QRS complex of the operator,

first and second gate means when enabled applying said error signal 'tosaid first and second input channels respectively,

means for enabling one or the other of said first and second gate meansdepending upon whether the output of said pulse stretcher means is lessthan or greater than the output of said adjustable pulse stretchermeans,

means for counting the number of trigger pulses in each group of triggerpulses for disabling said first and second gate means whenever thenumber of pulses counted as less than or greater than a predeterminednumber of pulses.

1. Apparatus for monitoring the physiological condition of an occupantof a motor vehicle during vehicle operation comprising; pickup means forsensing an electrical signal related to the physiological condition ofthe vehicle occupant, signal conditioning means connected with saidpickup means, rectifier means connected with said signal conditioningmeans for developing an output pulse corresponding to each excursion ofthe conditioned signal above and below respective upper andlower-voltage levels, pulse generating means for generating a triggerpulse train corresponding to the leading and trailing edge of eachoutput pulse, pulse stretcher means responsive to said trigger pulsetrain for developing a pulse of duration greater by a fixed timeinterval than the duration of said trigger pulse train, adjustable pulsestretcher means responsive to the first pulse in said trigger pulsetrain for developing a pulse of adjustable duration, comparator meansresponsive to the output of said fixed and adjustable pulse stretchersfor developing an error pulse output of duration proportional to thedifference in the duration of the output of said fixed and adjustablepulse stretcher means, means including ratiometer means responsive tosaid error signal for indicating the magnitude and polarity of saiderror signal, means for manually adjusting the output of said adjustablepulse stretcher to produce a null output from said ratiometer meanswhereby said ratiometer indicates any significant change in the width ofthe output signal of said signal conditioning means subsequent toadjustment of said adjustable pulse stretcher, means for counting thenumber of pulses in said trigger pulse train and for inhibiting theoutput of said fixed and adjustable pulse stretchers when the number ofpulses in said pulse train are less than or greater than a predeterminednumber.
 2. In a motor vehicle provided with a steering wheel, apparatusfor monitoring the electrocardiac signal of the operator of the vehicleand for indicating to said operator a change in said signal from thenominal signal of the operator, said apparatus comprising; a pair ofelectrodes mounted in said steering wheel for sensing the electrocardiacsignal present between the hands of the operator, signal conditioningmeans comprising first and second amplifiers having their non-invertinginputs connected with respective ones of said electrodes, a capacitorinterconnecting the inverting inputs of said first and secondamplifiers, a resistance-capacitance network interconnecting the outputof each of said first and second amplifiers to their respectiveinverting inputs, a third amplifier having its respective non-invertingand inverting inputs capacitively coupled to said first and secondamplifiers, a third resistance capacitance network interconnecting theoutput and inverting input of said third amplifier, full-wave rectifiermeans comprising first and second level detecting means responsive tothe output of said signal conditioning means for developing a pulsetrain containing a pulse for each excursion of the input signal aboveand below a positive and a negative voltage level, pulse generatingmeans for developing a trigger pulse corresponding to each of theleading and trailing edges of said pulse train, pulse stretcher meanscomprising a single shot multivibrator triggerable to a semi-stablestate in response to a trigger pulse from said pulse generator means andreturning to its stable state a fixed interval of time thereafter, asecond single shot multivibrator triggerable to its semi-stable state inresponse to the triggering of said first single shot multivibrator andreturning to its stable state after an adjustable time interval,differential power ratiometer means comprising first and secondchannels, gating and storage means responsive to the state conditions ofsaid first and second monostable multivibrators for developing an errorsignal for application to one or the other of said first and secondchannels depending upon which of said monostable multivibrators firstreturns to its stable state and proportional to the difference in theduration of the unstable state of said first and second monostablemultivibrators, means for counting the number of trigger pulses fromsaid pulse generator and for inhibiting said gating means when thenumber of trigger pulses are less than or greater than a predeterminednumber.
 3. In a motor vehicle provided with a steering wheel, apparatusfor monitoring for any change in the electrocardiac signal of theoperator of the motor vehicle during vehicle operation comprising firstand second electrodes mounted in said steering wheel for sensing theelectrocardiac sigNal existing between the hands of the vehicleoperator, signal conditioning means comprising amplifying and filteringmeans connected across said electrodes for developing a scaled versionof the QRS complex of said electrocardiac signal, means including fullwave rectifying means and pulse generating means for developing a groupof trigger pulses over an interval of time related to the width of theQRS complex of said electrocardiac signal, pulse stretcher meansresponsive to said trigger pulses for developing a pulse of durationgreater by a fixed time interval than the duration of said group oftrigger pulses, adjustable pulse stretcher means responsive to the firstpulse in said group of trigger pulses for developing a pulse of durationcorresponding to the nominal width of the QRS complex of theelectrocardiac signal of the vehicle operator, comparator meansresponsive to the output of said fixed and adjustable pulse stretchersfor developing a pulse output of duration proportional to the differencein the duration of the QRS complex being monitored and the nominal QRScomplex of the vehicle operator, error amplifying means connected withsaid comparator means, indicator means having first and second inputchannels and providing an indication of the average magnitude anddirection of any deviation of the sensed QRS complex from the nominalQRS complex of the operator, first and second gate means when enabledapplying said error signal to said first and second input channelsrespectively, means for enabling one or the other of said first andsecond gate means depending upon whether the output of said pulsestretcher means is less than or greater than the output of saidadjustable pulse stretcher means, means for counting the number oftrigger pulses in each group of trigger pulses for disabling said firstand second gate means whenever the number of pulses counted as less thanor greater than a predetermined number of pulses.